Mobile phones, personal digital assistants (“PDAs”), digital cameras, MP3 players, and other portable electronic devices utilize SSL devices (e.g., white light LEDs) for background illumination. SSL devices are also used for signage, indoor lighting, outdoor lighting, and other types of general illumination. However, true white light LEDs are not available because LEDs typically only emit at one center wavelength. For human eyes to perceive the color white, a mixture of wavelengths is needed.
One conventional technique for emulating white light with LEDs includes depositing a converter material (e.g., a phosphor) on an LED die. FIG. 1A shows a conventional SSL device 10 that includes a support 2 carrying an LED die 4 and a converter material 6. As shown in FIG. 1B, the LED die 4 can include a substrate 12, an N-type gallium nitride (GaN) material 14, GaN/indium gallium nitride (InGaN) multiple quantum wells (“MQWs”) 16, a P-type GaN material 18, a first contact 20, and a second contact 22.
Referring to both FIGS. 1A and 1B, in operation, an electrical voltage is applied between the first and second contacts 20 and 22. In response to the applied voltage, the GaN/InGaN MQWs 16 of the LED die 4 produce a first emission (e.g., a blue light) that stimulates the converter material 6 to emit a second emission (e.g., a yellow light). The combination of the first and second emissions appears white to human eyes if matched appropriately. As discussed in more detail below, using converter materials to “convert” blue light into white light has certain drawbacks. Accordingly, several improvements in producing white light SSL devices without converter materials may be desirable.